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Altera_Forum's avatar
Altera_Forum
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15 years ago

Do you use LPMs for your LFSRs?

I want to implement an LFSR as a means of generating random numbers but I'm not sure whether to use an LPM or just code it in a process. I would be interested to hear how you choose to implement them...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

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Thanks again Kaz. I can't quite see where I was going wrong 


process(reset,clock)
begin
if reset = '1' then
   shift_reg <= "0001"; -- seed
elsif rising_edge(clock) then
   shift_reg(1) <= shift_reg(0) XOR shift_reg(3); -- taps
   shift_reg(2) <= shift_reg(1); -- shift
   shift_reg(3) <= shift_reg(2);
end if;
output    <=    shift_reg;
end process;
When I simulate this the output is always 1?

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This is a perfect implementation of 4-bits LFSR. If it stays at 1, check your reset signal.

Good luck, Ton